In the past, a chemical-mechanical polishing (CMP) process was developed for planarization of semiconductor surfaces and metal inlays during manufacturing. A chemical, a base or neutral for semiconductor oxide surfaces and an acid for metals, with a number of other proprietary chemicals would be used to soften the surface material and an abrasive, such as alumina or silicon, would be used for planarization in a machine called a polisher. The chemicals have a pH range of 2 to 11 and carry the abrasive in suspension as a slurry which is kept constantly in motion to prevent separation.
As semiconductor devices were reduced in size, it became desirable to use CMP processing to obtain increasingly flat surfaces. As CMP came to be used in semiconductors with line geometries of 0.35 micron, it became common to provide filtration systems to control the size of particles reaching the polisher in order to reduce the defects caused by particle scratches. Smaller particles cause smaller scratches but with smaller line geometries, the smaller scratches still negatively affect the final semiconductor device. With sub-0.35 micron semiconductor devices, filtration systems are universally used either as part of the recirculating system for the slurry or directly in the line to the polisher.
The problem with current filtration systems is that they must compromise between the particle size that can be filtered out and the time between replacement of the filter. For example, the smaller the particle size filtered, the sooner the filter must be replaced. This filter replacement interrupts production for a significant amount of time and reduces the number of semiconductor devices which can be produced. Conversely, allowing larger particles to the polisher for longer filter life results in increased defects which also reduces the number of semiconductor devices which can be produced even though production can continue longer without interruption.
A solution, which would allow continuous filtration of small particles, has long been sought, but has also long eluded those skilled in the art. Such a solution would be highly valuable since the economics of semiconductor production equate small improvements in production to large sums of money because of the high selling price of semiconductor devices.